Method of making potassium hydroxid.



UNITED STATES PATENT Curios.

HEINRICH PREGHT, O-F NEUSTASSFURT, GERMANY.

METHob OF MAKING POTASSIUM HYDROXID.

SPECIFICATION forming part of Letters Patent No. 665,617, dated January8, 1901.

Application filed July 23, 1900. Serial No. 24,620. (No specimens.)

To all whom it may concern.-

Be it known that I, HEINRICH PREOHT, a subject of the King of Prussia,German Emperor, and a resident of Neustassfurt, Germany, have inventedcertain new and useful Improvements in and Relating to the Prod uctionof Potassium Hydrate; and I do hereby declare the following to be afull, clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

This invention relates to a method for purifying potassium hydrate, andespecially for separating from it potassium chlorid, which is a commonimpurity, especially when the hydrate has been produced electrolyticallyfrom the chlorid. The relative solubility of the base and salt forms thebasis of separation. If a solution of potassium hydrate containingpotassium chlorid be evaporated, the chlorid will separate out, leavinga solution containing fifty per cent. hydrate with 0.55 per cent.chlorid still in' the solution. These figures correspond to solubilitiesat from 15 to 20 centigrade, and from this solution a product isobtained which contains for one hundred parts, by Weight, of KOH about1.10, by weight, of KGl. Such a product is not pure enough for somepurposes, and the object is to obtain one of as high purity as possible.

From the above results it was thought that by using a solution of higherconcentrationsay, of sixty per cent. KOHa more complete separation ofthe K01 could be obtained; but it was found that with such aconcentration and the aid of recrystallization at normal temperature amore complete separation could not be obtained. A crystalline productwas obtained which contained sixty-four per cent. KOH and 0.64 per cent.K01, or for every one hundred parts, by weight, of KOH there remainedone part,byweight,KOl. These figures difier very little from theprevious values obtained from the fifty-per-cent. solution and arelikewise unsatisfactory. In a similar manner purification bycrystallization was carried out at 0 centigrade; but the result wasequally unsatisfactory. After unfruitful experiments I attempted toseparate the two substances by holding the chlorid in solution andcrystallizing out the hydrate at higher temperatures, and although thesolubility of potassium hydrate is greater at higher temperatures Isucceeded. The desired separation can therefore be obtained as follows:An approximately fifty percent. potassium-hydrate solution containingabout 0.55 per cent. or half a per cent. of potassium chlorid asimpurity is evaporated until the hydrate crystals begin to separate,when the solution is continually stirred, either by hand or in amechanical stirrer, and then cooled to about 60 centigrade, whereby arapid crystallization takes place. The crystals are then separated fromthe mother-liquor in any desired manner, as by a centrifugal machine,and washed with a small quantity of water. The

temperature can be allowed to drop as low as 35 centigrade during theseparation of the crystals from the mother-liquor without seriousconsequences; but below this temperature a high purification is notpossible because of the separation of the chlorid. The resultingcrystals contain about seventy per cent. KOH and 0.073 per cent. K01, orin every one hundred parts, by weight, of KOH there will be 0.104 parts,by weight, of KCl. It is thus possible to operate on a commercial scalea process for purifying the hydrate from chlorid with results notheretofore obtained.

Having now particularly described my invention, what I claim as new, anddesire to secure by Letters Patent, is-

1. The process which consists in evaporating a solution containing aboutfifty per cent. of potassiumhydrate and about half a per cent. ofpotassium chlorid, allowing the crystals to separate out at aboutcentigrade and removing the crystals, substantially as described.

2. The process which consists in evaporating a solution containing aboutfifty per cent. of potassium hydrate and about half a per cent. ofpotassium chlorid, crystallizing out the hydrate at about 60 centigrade,and removing the crystals from the mother-liquor at a temperature notless than 35 centigrade, substantially as described.

3. The process which consists in evaporating a solution of potassiumhydrate and potassium chlorid, separating the latter at a In testimonythat I claim the foregoingas temperature of from about 15 to 20 centimyinvention Ihave signed my namein presgrade, evaporating the remainingsolution, ence of two subscribing witnesses.

stirring and cooling the same to about 60 HEINRICH PRECHT. 5 centigrade,and removing the crystals formed Witnesses:

at a temperature notless than 35 centigrade, GEORGE H. MURPHY,

substantially as set forth. CARL OS'IERMANN.

